Figure 3. Cluster Size and Centrality of Smokers Across Time.

(a) Smokers remained in tightly-knit groups, even as the incidence of smoking sharply declined. Marginal smokers are not leaving smoking groups; instead, whole clusters are quitting and those that are not maintain their previous size. (b) Eigenvector centrality computed at each wave for smokers and non-smokers. While the centrality of non-smokers remains roughly stable across all waves, smokers become increasingly less central, and more peripheral, in the social network. Bars in both panels show 95% confidence intervals. In the left panel, confidence intervals are too small to see (the largest is slightly larger than the height of the dark squares). Both panels exclude neighbor and co-worker ties.